Duchenne muscular dystrophy (DMD) is a severe muscle wasting disease associated with the loss of functional dystrophin, a protein essential for sarcolemmal stability. Extraocular muscles (EOMs) are uniquely unaffected by dystrophin deficiency in humans and in animal models. Specific traits of EOM satellite cells (SCs, adult myogenic progenitors) may play a role in EOM preferential sparing. This exploratory project aims to evaluate the potential of EOM SCs as effective source for cell-based therapy to combat DMD. Our mouse studies showed superiority of freshly isolated EOM vs. limb SCs, in engraftment potential and ex-vivo expansion capability. Impressively, EOM SCs established numerous renewal cells that maintain vigorous expansion ability upon re-culturing. Hence, the use of EOM SCs as a source for donor myoblasts could allow bypassing the limited expansion capacity encountered with limb SCs, and meeting the demand for a high number of progenitors essential for clinical applications. Significantly, a protocol can be developed eventually for human EOM retrieval in a manner similar to current Eye Bank operations. It is important however to determine first if EOM SCs or their progeny would continue to maintain their high-performance capacity in dystrophin-deficiency affected (limb) host environment. The proposed studies will also provide key data about the outcome of myogenic cell engraftment to newly born pups compared with the more traditional engraftment paradigm to older animals. As newborn screening of DMD is entering the clinics, identifying means for myoblast replacement soon after birth is of importance. In the proposed studies, donor SCs isolated from EOMs of adult mice will be transplanted into muscles of dystrophin-deficient (mdx4cv) host mice. Transplantation outcome will be determined by monitoring donor-derived reporter expression, restoration of dystrophin in the sarcolemma, extent of central myonuclei and muscle performance. Accordingly, the specific aims of this application are: 1. Investigate engraftment outcome following intra- muscular delivery of donor EOM SCs injected to newly born (3-day-old) and newly weaned (24-day-old) host mdx mice. Emphasis is given to short-term (at 6 & 12 weeks of age) and long-term (at 24 & 48 weeks of age) engraftment outcomes. 2. Refine means for ex-vivo expansion of EOM SC progeny and investigate in- vivo engraftment outcomes with the expanded cells (as in Aim 1). It is recognized that while the mdx mouse has been used extensively as a laboratory model of DMD, the mdx pathology is far less severe than that of DMD patients. Still, studies with mdx mice have generated important directive data for subsequent studies with dystrophic dogs and for pilot clinical trials in human. I am confident that the approaches considered herein will be successful in contributing new insights toward novel clinical approaches for combating DMD and other muscle wasting conditions.